They don’t usually use real water jets, but instead use fans to “blow” the air around (also because of the 120 volt outlet), which causes them to cool down much faster than a regular hot tub. This cooling effect is only made worse by the fact that the materials they are made from lose heat much faster than the materials used on a regular hot tub. All in all, you aren’t likely to get more than 15 minutes to a half an hour of good heat out of an inflatable hot tub.